CN113073485B - A kind of preparation method of nanocellulose fiber and product thereof - Google Patents

Abstract

The invention relates to the technical field of nano-cellulose, in particular to a preparation method of nano-cellulose fiber and a product thereof; specifically, crop straws are used as raw materials, steam flash explosion treatment is carried out on the raw materials, then high-pressure homogenization is carried out, and then lignin and hemicellulose are removed to obtain the nano cellulose fibers. The data obtained by the Box-Behnken experiment are processed by Design-expert.V8.0.6 software, and the optimal steam flash explosion conditions are obtained as follows: the steam flash explosion pressure value is as follows: 1.52MPa, and the steam flash explosion time is as follows: 283.31s, sodium hydroxide concentration: 1.59 wt%, the nanocellulose yield obtained under these conditions was: 46.02 percent. The invention provides reference for optimizing steam flash explosion process parameters and improving the preparation and research of the yield of the nano-cellulose, and lays a foundation for further research of the nano-cellulose.

Description

A kind of preparation method of nanocellulose fiber and product thereof

technical field

The invention relates to the technical field of nanocellulose, in particular to a preparation method of nanocellulose fibers and a product thereof.

Background technique

Nanocellulose refers to the cellulose in nanomaterials in which at least one dimension is in the nanoscale (1-100 nm), and the nanomaterials can be dispersed in water to form cellulose crystals in stable suspensions. According to the morphology, particle size, and different sources of nanocellulose, nanocellulose can be roughly divided into the following three categories: ①Microfibrillated cellulose (MFC) ②Nanocellulose crystals (Cellulose whisker) ③Bacteria Nanocellulose (Bacterial cellulose, BC). The preparation of nanocellulose from plants can be divided into two categories according to the crystal form: nanocellulose fibers or microfibrillated cellulose (Nanofibrillated cellulose, NFC) and nanocrystalline cellulose (Nanocrystalline cellulose, CNC). Compared with the short rod-like structure of CNC, NFC has a larger aspect ratio and specific surface area, high crystallinity, good hydrophilicity, and strong spatial expansion. It is a new type of nanomaterial, which has good application prospects in food processing, medicine and other fields.

According to the investigation, the annual production of corn stalks in my country is about 170 million tons. With the rapid development of the planting industry, a large amount of straw is accumulated, and people have to burn it. The burning of a large amount of straw produces a large amount of PM2. Large areas of the environment are polluted. How to rationally utilize corn stalk resources has become a major problem that people are facing today. Corn stover is rich in cellulose, hemicellulose and lignin, and the crude fiber content is as high as 31%-41%. Therefore, it would be very economical to provide a method for preparing nanocellulose fibers (NFC) from crop straws.

SUMMARY OF THE INVENTION

Based on the above content, the present invention provides a method for preparing nanocellulose fibers and a product thereof. By using crop straws as raw materials and preparing nanocellulose fibers by steam explosion treatment, the effective utilization of waste resources is realized under the premise of energy saving and environmental protection.

One of the technical solutions of the present invention is a method for preparing nanocellulose fibers, which uses crop straws as raw materials, undergoes steam flash explosion treatment, high-pressure homogenization, and then removes lignin and hemicellulose to obtain nanocellulose fibers.

Steam flash explosion is a technology that uses high-temperature and high-pressure water vapor to instantaneously release pressure to separate substances. The process of steam flash explosion is divided into four stages: (1) Class acid hydrolysis and thermal degradation; (2) ) class mechanical fracture; (3) hydrogen bond destruction; (4) structural rearrangement. The invention utilizes steam flash explosion to treat crop straw to destroy the structure of lignocellulose through high-strength force, so that cellulose, hemicellulose and lignin are better separated, thereby facilitating the extraction of nanocellulose fibers.

Further, the crop straws are soaked in sodium hydroxide solution before steam flash explosion.

The cellulose in the straw raw material treated with sodium hydroxide did not increase significantly, but the content of hemicellulose and lignin changed significantly, because the hemicellulose in the straw would have a peeling reaction with the lye , the cellulose glycosidic bond is hydrolyzed and cleaved, and the acetyl group on the hemicellulose molecule is also easy to fall off. The phenolic hydroxyl group in the lignin molecular structure is cleaved when it reacts with NaOH, thereby increasing the solubility of the lye and making the The reaction is efficient and orderly. The alkali treatment before the steam flash explosion also makes the cellulose swell under the condition of high temperature alkali treatment, which is more conducive to the separation of hemicellulose and lignin.

Further, the concentration of the sodium hydroxide solution is 1.0-2.0wt%, and the soaking time is 24h.

Further, the steam flash explosion treatment conditions: pressure 0.5-2.5MPa, time 90-360s.

Further, the concentration of sodium hydroxide solution is 1.59wt%, the steam flash explosion pressure is 1.52MPa, and the steam flash explosion time is 283.31s. Under these conditions, the highest yield of nanocellulose fibers is 46.02%.

Further, the following steps are specifically included:

(1) cutting off the crop straw, drying after washing, pulverizing and sieving 80 meshes, soaking in sodium hydroxide solution and performing steam flash explosion, filtering, washing and drying after 40MP high pressure homogenization for 6 times to obtain a straw sample;

(2) place the straw sample obtained in step (1) in an aqueous solution containing sodium chlorite and acetic acid and heat treatment until the solution turns white, filter, wash, and dry;

(3) The product obtained in step (2) is placed in an alkaline solution and then heated, washed with water and air-dried to obtain nanocellulose fibers.

The steam flash treatment not only helps to produce more cellulose, but also can remove a certain amount of hemicellulose and lignin, because the steam flash treatment can make the straw silken, so that the cellulose and hemifibers that were originally intertwined Separation of hemicellulose and lignin for easier removal of hemicellulose and lignin in subsequent experiments. High-pressure homogenization can convert cellulose into nanocellulose with smaller particle size after strong shearing and high-pressure treatment, and hemicellulose and lignin will not change during the process.

Further, in the step (2), the heating treatment temperature is 75°C, and during the heating treatment, sodium chlorite and acetic acid are added every 1 h.

Further, in the step (3), the alkaline solution is specifically a potassium hydroxide solution with a mass concentration of 6%, which is left standing at room temperature for 8 hours and then placed in an environment of 80° C. for heat treatment for 2 hours.

Further, the crop straw is corn straw or wheat straw.

The second technical solution of the present invention is the nanocellulose fibers prepared by the above-mentioned preparation method of nanocellulose fibers, wherein the nanocellulose fibers are slender fibers with a diameter of 20-220 nm. The smaller diameter makes the water solubility of nanocellulose better.

Compared with the prior art, the present invention has the following beneficial effects:

The invention forms cellulose with nanometer diameter by using crop straw as raw material, through alkali pretreatment, steam explosion and high pressure homogenization treatment, and achieves the technical purpose of maximizing the yield of nanocellulose fibers. Through the data obtained from the Box-Behnken experiment and processed by the Design-Expert.V8.0.6 software, the optimal steam flash explosion conditions are obtained: the steam flash explosion pressure value is: 1.52MPa, and the steam flash explosion time is: 283.31s , the concentration of sodium hydroxide is: 1.59wt%, and the yield of nanocellulose obtained under this condition is: 46.02%. In order to verify the feasibility of the response surface method, and considering the specific feasibility of the experiment during the operation, the steam flash explosion pressure is 1.5MPa, the steam flash explosion time is 285s, the sodium hydroxide concentration is 1.6%, and the conditions Confirmatory experiments were carried out under the following three groups of parallel experiments, and the obtained nanocellulose was 45.88%, and the error with the predicted value of 46.02% was within 1.5%, indicating that the process parameter model obtained by the response surface optimization is reliable, and it is suitable for It is of certain significance to improve the yield of nanocellulose. It provides a reference for the preparation and research of optimizing the steam flash explosion process parameters to improve the yield of nanocellulose, and lays a foundation for further research on nanocellulose.

Description of drawings

Fig. 1 is the influence of sodium hydroxide concentration on straw composition in embodiment 1;

Fig. 2 is the influence of steam flash explosion pressure on straw composition in Example 1;

Fig. 3 is the influence of steam flashing time on straw composition in Example 1;

Fig. 4 is the three-dimensional surface graph and the contour map of the effect of steam flash explosion pressure and steam flash explosion time on cellulose content in Example 1;

Fig. 5 is the three-dimensional surface map and contour map of the influence of steam flash explosion pressure and sodium hydroxide concentration on cellulose content in Example 1;

Fig. 6 is the three-dimensional surface map and contour map of the effect of steam flash time and sodium hydroxide concentration on cellulose content in Example 1;

FIG. 7 is a transmission electron microscope image of nanocellulose in Example 1. FIG.

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail, which detailed description should not be construed as a limitation of the invention, but rather as a more detailed description of certain aspects, features, and embodiments of the invention.

It should be understood that the terms described in the present invention are only used to describe particular embodiments, and are not used to limit the present invention. Additionally, for numerical ranges in the present disclosure, it should be understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention relates. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials in connection with which the documents are referred. In the event of conflict with any incorporated document, the content of this specification controls.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the present invention. The description and examples of the present application are only exemplary.

As used herein, "comprising," "including," "having," "containing," and the like, are open-ended terms, meaning including but not limited to.

In the following examples of the present invention:

Materials and Reagents

Corn stalks (Kerui 981, taken from farmers in Daqing City). EDTA was provided by Ronghong Chemical Co., Ltd.; Acetone was provided by Fuyu Fine Chemical Co., Ltd.; Sodium Dodecyl Sulfonate and Cetyl Trimethyl Ammonium Bromide were provided by Shanghai Kaiyin Chemical Co., Ltd. ; Ethylene glycol ether is provided by Huaxin Chemical Company; Sodium Tetraborate Decahydrate is provided by Shanghai Fusheng Industrial Co., Ltd.;

Instruments and Equipment

PHS.2C type precision pH meter is from METTLER TOLEDO company in the United States; FZ102 micro plant grinder is from Tianjin Tester company; AB204-N analytical balance is from Shanghai METTLER-Toledo Instrument Co., Ltd.; TDZ5-WS type multi-tube The automatic balancing centrifuge is from Changsha Xiangyi Centrifuge Instrument Co., Ltd.; the SENCO constant temperature water bath is from Shanghai Shensheng Technology Co., Ltd.; The homogenizer was from Ruofan Industrial Systems Co., Ltd.; the JEM-200CX transmission electron microscope was from JEOL Corporation of Japan.

Example 1

(1) Cut the corn stalks, wash them, dry them, pulverize and sieve them to 80 mesh, soak them in 100 mL of sodium hydroxide solution for 24 hours, and then perform steam flash explosion, filter, wash, and dry to obtain straw samples, which are placed in a Processing in a high-pressure homogenizer can refine the fibers and facilitate the next step.

(2) Removal of lignin: take 2g of straw residue, add 130ml of deionized water, 1.2g of sodium chlorite, and 1ml of acetic acid, shake well, seal it and place it in a water bath at 75 degrees Celsius for 1 hour, and add 1.2g of chlorite every 1 hour. Sodium, 1ml acetic acid until the solution turns white, stop heating, wash with deionized water until neutral, and dry [11-12].

(3) Removal of hemicellulose: put the residue into 300ml of KOH solution with a concentration of 6%, let it stand at room temperature for 8 hours, then heat it in a water bath at 80°C for 2 hours, wash it with deionized water until it becomes neutral, and dry it in the air.

Wherein, the steam explosion condition in step (1) selects single factor experiment, concrete:

The pressure is maintained at 2.0MPa, the blasting time is 270s, and the mass fraction of sodium hydroxide concentration is 0.5%, 1.0%, 1.5%, 2.0%, 2.5%;

And, blasting is carried out at 0.5MPa, 1.0MPa, 1.5MPa, 2.0MPa, 2.5MPa, and the lower dimension pressure is 270s;

And, under the condition that the pressure is maintained at 2.0 MPa, the straw raw materials are treated for 90 s, 180 s, 270 s, and 360 s, respectively.

Effect verification

1. Analyze the cellulose, hemicellulose, lignin content of the embodiment through different treatments and steam explosion, and the analysis method is as follows:

1.1 Reagent preparation

Neutral reagent configuration: Weigh 18.61g of ethylenediaminetetraacetic acid and mix with 6.81g of sodium tetraborate decahydrate, add 250mL of distilled water and put it into a water bath for dissolution (recorded as 1 solution), add 30g of dodecylbenzenesulfonic acid Add 200 mL of distilled water to the sodium, and gradually add 10 mL of ethylene glycol ether and 4 g of NaOH, heat on a water bath until dissolved (recorded as 2 liquids), add 150 mL of distilled water to 4.56 g of sodium dihydrogen phosphate and place it on a water bath for heating (Denoted as 3 liquids), mix 1 liquid, 2 liquids and 3 liquids, adjust the pH to be in the range of 6.9-7.1, and add water to make up to 1000 mL.

Configuration of acidic reagent: take 20 g of cetyl trimethyl ammonium bromide and dilute to 1000 mL with 1 mol/L sulfuric acid.

1.2 Determination of cellulose, hemicellulose and lignin content

The content of cellulose and hemicellulose was determined by the paradigm fiber assay.

The above straw powder was placed in a water bath at 80 °C for 1 hour, and then placed in a 60 °C oven for drying. 1 g of straw powder was placed in a flat-bottomed flask (marked as m), and 0.5 g of anhydrous sodium sulfite, 100 mL of neutral reagent and Put a few drops of acetone on the electric furnace to heat, start timing after boiling, heat and reflux for 1 hour, then carry out suction filtration, and rinse with boiling water, the number of times is not less than 2 times, rinse with 30mL distilled water each time, and then rinse with acetone, the number of times No less than 2 times, 20 mL of acetone was used for washing each time, and the obtained straw powder was placed in an oven at 80° C. for drying (referred to as m ₁ ).

The powder (m ₁ ) obtained after drying was placed in a flat-bottomed flask, and 100 mL of an acidic reagent and a few drops of isooctanol were added for heating and refluxing. After boiling, the timer was started. The time should not be less than 1 hour. Wash twice, wash twice with acetone, collect all the residues, put them in an oven for drying (denoted as m ₂ ). The straw powder (m ₂ ) was placed in 5 mL of 75% sulfuric acid added, placed in a 50°C water shaker for hydrolysis for 12 hours, filtered while hot, washed twice with boiling water, washed twice with acetone, and then placed It was dried in an oven to obtain straw powder (denoted as m ₃ ).

Hemicellulose and cellulose are calculated as follows:

Hemicellulose (%)=(m ₁ -m ₂ )/m×100% (1);

Cellulose (%)=(m ₂ -m ₃ )/m×100% (2);

The determination of the lignin content adopts the Klason method, which is specific to the prior art, and will not be repeated here.

1.3 Analysis of results

(1) Influence of sodium hydroxide concentration

As shown in Figure 1, the cellulose of the straw raw material treated with sodium hydroxide did not increase significantly, but the content of hemicellulose and lignin changed significantly, because the hemicellulose in the straw would interact with the straw. The lye undergoes a peeling reaction, in which the cellulose glycosidic bonds are hydrolyzed and cleaved, and the acetyl groups on the hemicellulose molecules are also easy to fall off. The solubility of the liquid makes the reaction efficient and orderly. The alkali treatment before the steam flash explosion also makes the cellulose swell under the condition of high temperature alkali treatment, which is more conducive to the separation of hemicellulose and lignin.

(2) Effect of steam explosion pressure on straw composition

It can be seen from Figure 2 that the content of cellulose increased significantly after steam flash explosion treatment, while the content of hemicellulose and lignin decreased. content showed a downward trend. When the steam pressure is 2.5MPa, the cellulose content increases from 32.65% to 39.14%, the hemicellulose content decreases from 27.16% to 15.32%, the lignin content decreases from 18.21% to 12.43%, and the hemicellulose and lignin content A total of 53.45% fell. When the steam pressure was 1.5MPa, only 2.34% of the hemicellulose in the straw was degraded. When the steam pressure increased to 2.0MPa, the content of hemicellulose began to decrease significantly by 3.83%. The reason for this result is that the high temperature makes the straw fiber more softened, and the high temperature decomposes part of the cellulose; it may also be that when the steam flash explosion pressure increases, the increase in the temperature of the water vapor in the explosion cavity produces a larger amount of water vapor. Due to the mechanical force of high temperature and high pressure, hemicellulose is hydrolyzed into acidic substances and dissolves in water. It is soluble in water, so even if the steam pressure is increased, the content of hemicellulose and lignin cannot be further reduced.

(3) Effect of steam flash explosion time on straw composition

It can be seen from Figure 3 that with the prolongation of the steam flash explosion time, the cellulose content in the straw gradually increases, and the content of hemicellulose and lignin gradually decreases. The time of steam flash explosion was increased from 90s-350s, the cellulose content increased from 32.03% to 38.01%, an increase of 5.98%, while the content of hemicellulose and lignin decreased from 27.7% and 20.68% to 15.84% and 12.25%, respectively. decreased by 11.86% and 8.43%, respectively. This is because in the process of steam flash explosion, with the extension of time, the hydrolysis time of hemicellulose is more sufficient, and the acidic environment formed after the hydrolysis of hemicellulose is conducive to the decomposition of lignin.

1.4 Optimization of response surface conditions

According to Box-Behnken's central combined experimental design principle, based on the single factor test results, with the steam flash pressure value (A), the steam flash time (B), and the sodium hydroxide concentration (C) as the response factors, the cellulose content is (Y) is the response value, using the response surface analysis method with 3 factors and 3 levels to conduct the experimental design. The factors and coding levels are shown in Table 1. Results Using Design-Expert.V8.0.6 software for data processing and response surface analysis.

Table 1

According to the Box-Behnken principle, 17 experimental groups with three factors and three levels were designed for the response surface optimization analysis test. The response surface test design and results are shown in Table 2. Use Design-Expert.V8.0.6 software to perform regression fitting analysis on the response value and the coding value of each factor, and obtain the quadratic multiple regression equation.

Y=45.92+0.7663A+0.6738B+0.3500C-1.46AB-1.53AC+1.46BC-4.33A ² -2.96B ² -1.49C ² . The results of the analysis of variance for the regression equation are shown in Table 3. As can be seen from Table 3, the regression equation model established for corn stalk nanocellulose has extremely high significance (P=0.0001), the lack of fit (P=0.0652>0.05) is not significant, and the adjustment coefficient of the model R ² = 0.9715, R ² _Adj = 0.9348, indicating that the model fits well with the actual experiment, the linear relationship between the independent variable and the response surface is more significant, and the experimental error is small, so the regression model can be used to analyze and predict corn stalks Process parameters with the highest cellulose content in nanocellulose.

It can be seen from the significance test of the regression equation coefficients in Table 3 that AC, A ² , B ² , and C ² in the model have extremely significant effects on the response surface (P<0.01), and A, C, AB, and BC have a significant impact on the response surface. (P<0.05), B and C had no significant effect on the response surface (P>0.05). In the regression equation, the coefficient value of each factor directly reflects the influence of each experimental factor and index value. From the mean square value of each factor, the order of influence of each factor on the cellulose content in corn stalk nanocellulose is as follows (steam flash pressure value (A), steam flash time (B), sodium hydroxide concentration (C) ): steam flash explosion pressure value (A) > steam flash explosion time (B) > sodium hydroxide concentration (C), the primary and secondary order of the interaction among the three factors is: AC>BC>AB.

Table 2

table 3

The interaction of the three factors of steam flash explosion pressure value, steam flash explosion time and sodium hydroxide concentration in the reaction process is shown in Figure 4-6. If the trend of the curve in the response surface is getting steeper, it indicates that the interaction between the two factors is more significant; if the curve of the response surface is smoother, it indicates that the interaction effect of the two factors is smaller; Factor interactions are significant, while circles indicate insignificant interactions.

It can be seen from Figure 4 that the contour lines are elliptical, indicating that the interaction between the steam flash pressure and the steam flash time is significant. When the steam flash pressure is less than 1.5MPa, the contour lines are dense, indicating that the steam flash pressure has a significant effect on the cellulose content of corn stover (p<0.05); when the steam flash pressure is 1.5-2MPa, the curve is relatively stable, and the The contour lines are sparse, indicating that with the continuous increase of the steam flash pressure, the value affecting the cellulose content becomes smaller and smaller. It can be seen from Figure 5 that with the increasing trend of the 3D image, the color gradually deepens and the slope becomes steeper, indicating that the interaction between the steam flash explosion pressure and the concentration of sodium hydroxide is significant (p<0.01). When the steam flash explosion pressure and the sodium hydroxide concentration are at 0 level, the cellulose content is larger and remains unchanged; when the steam flash explosion pressure and the sodium hydroxide concentration are lower than 0 level, the cellulose content increases with the two. The increase of the number of people increased, and showed a more obvious upward trend. It can be seen from Figure 6 that there is a significant interaction between the steam flash explosion time and the sodium hydroxide concentration. With a fixed sodium hydroxide concentration, the cellulose content shows a trend of first rapid increase and then slow decline with the increase of the steam flash explosion time. , at the same steam flash explosion time, the cellulose content decreased with the increase of sodium hydroxide concentration.

Through the data obtained from the Box-Behnken experiment and processed by the Design-Expert.V8.0.6 software, the optimal steam flash explosion conditions are obtained: the steam flash explosion pressure value is: 1.52MPa, and the steam flash explosion time is: 283.31s , the concentration of sodium hydroxide is: 1.59wt%, and the content of nanocellulose obtained under this condition is: 46.02%. In order to verify the feasibility of the response surface method and considering the specific feasibility of the experiment during the operation, the steam flash explosion pressure is 1.5MPa, the steam flash explosion time is 285s, the sodium hydroxide concentration is 1.6%, The confirmatory experiment was carried out under the conditions. By repeating 3 sets of parallel experiments, the content of nanocellulose obtained was 45.88%, and the error with the predicted value of 46.02% was within 1.5%, indicating that the process parameter model obtained by the response surface optimization was reliable. It has certain significance to improve the yield of nanocellulose.

2. Micro-morphology analysis

The samples prepared under the conditions of the steam flash pressure value of 1.5MPa, the steam flash explosion time of 285s, and the sodium hydroxide concentration of 1.6% were ultrasonically treated for 30min to make them evenly dispersed, and an appropriate amount of the sample was placed on a 400 mesh copper mesh. After drying, the samples were observed under a transmission electron microscope, and the TEM image of the nanocellulose was shown in Figure 7. It can be seen from Figure 7 that the nanocellulose is slender and fibrous with a diameter of 20-220 nm, which also shows that after steam flash explosion and high pressure averaging treatment, cellulose with nanometer diameter is formed, while the smaller cellulose is formed. The diameter makes the water solubility of nanocellulose better.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. within.

Claims (4)

1. A preparation method of nano cellulose fiber is characterized in that crop straws are used as raw materials, steam flash explosion treatment is carried out on the raw materials, then high-pressure homogenization is carried out, and then lignin and hemicellulose are removed to obtain the nano cellulose fiber;

the method specifically comprises the following steps:

(1) cutting crop straws, cleaning, airing, crushing, sieving by a 80-mesh sieve, soaking in a sodium hydroxide solution, performing steam explosion, filtering, washing, drying, and homogenizing under high pressure to obtain a straw sample;

(2) putting the straw sample obtained in the step (1) into an aqueous solution containing sodium chlorite and acetic acid, heating until the solution turns white, filtering, washing with water and drying in the air;

(3) placing the product obtained in the step (2) in an alkaline solution, standing, heating, washing with water, and drying to obtain nano cellulose fibers;

the crop straw is corn straw or wheat straw;

the concentration of the sodium hydroxide solution is 1.0-2.0 wt%, and the soaking time is 24 h;

the steam flash explosion treatment conditions are as follows: the pressure is 0.5-2.5MPa, and the time is 90-360 s.

2. The method for preparing nano cellulose fibers according to claim 1, wherein the heating temperature in the step (2) is 75 ℃, and sodium chlorite and acetic acid are added every 1 hour in the heating process.

3. The method for preparing nano cellulose fibers according to claim 1, wherein the alkaline solution in the step (3) is potassium hydroxide solution with a mass concentration of 6%, and the solution is left to stand at normal temperature for 8 hours and then is heated at 80 ℃ for 2 hours.

4. Nanocellulose fibers produced by the method of production of nanocellulose fibers according to any one of claims 1 to 3, wherein said nanocellulose fibers are in the form of elongated fibers having a diameter of 20 to 220 nm.

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